How to learn from my coworkers?

I work for a Chinese company (Lenovo), in the US. As a result, there are numerous international assignees (including my boss) from China at any given time. How should I take best advantage of their presence? Should I try something formal like a Chinese conversation club? Or should I limit it to informal (but as regular as possible) chit-chat in Chinese? I certainly don't want to abuse the friendship, but I also don't want to stagnate.

What think ye?

Jimmy, who hasn't yet figured out how to change his public profile name from user1890...